joppe/fpga_modem
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Compare commits

base: joppe:master
Branches Tags
joppe:master joppe:remotesyn
..
compare: joppe:remotesyn
Branches Tags
joppe:master joppe:remotesyn

1 Commits
master ... remotesyn

Author SHA1 Message Date
Joppe Blondel
85d9979e2d Added decimation 2025-10-19 17:19:08 +02:00
5 changed files with 64 additions and 135 deletions
Expand all files Collapse all files

2
project.cfg
View File

@@ -22,7 +22,6 @@ files_verilog = rtl/toplevel/top_generic.v
rtl/core/nco_q15.v rtl/core/nco_q15.v
rtl/core/sigmadelta_sampler.v rtl/core/sigmadelta_sampler.v
rtl/core/sigmadelta_rcmodel_q15.v rtl/core/sigmadelta_rcmodel_q15.v
rtl/core/sigmadelta_input_q15.v
rtl/core/mul_const.v rtl/core/mul_const.v
rtl/core/lpf_iir_q15_k.v rtl/core/lpf_iir_q15_k.v
rtl/core/decimate_by_r_q15.v rtl/core/decimate_by_r_q15.v
@@ -52,7 +51,6 @@ files_verilog = sim/tb/tb_nco_q15.v
rtl/core/nco_q15.v rtl/core/nco_q15.v
rtl/core/lvds_comparator.v rtl/core/lvds_comparator.v
rtl/core/sigmadelta_rcmodel_q15.v rtl/core/sigmadelta_rcmodel_q15.v
rtl/core/sigmadelta_input_q15.v
rtl/core/mul_const.v rtl/core/mul_const.v
rtl/core/lpf_iir_q15_k.v rtl/core/lpf_iir_q15_k.v
rtl/core/decimate_by_r_q15.v rtl/core/decimate_by_r_q15.v

58
rtl/core/sigmadelta_input_q15.v
View File

@@ -1,58 +0,0 @@
`timescale 1ns/1ps
module sigmadelta_input #(
parameter integer R_OHM = 3300,
parameter integer C_PF = 220
)(
input wire clk_15,
input wire resetn,
input wire adc_a,
input wire adc_b,
output wire adc_o,
output wire signed [15:0] signal_q15,
output wire signal_valid
);
`include "rc_alpha_q15.vh"
wire sd_signal;
wire signed [15:0] raw_sample_q15;
wire signed [15:0] lpf_sample_q15;
sigmadelta_sampler sd_sampler(
.clk(clk_15),
.a(adc_a), .b(adc_b),
.o(sd_signal)
);
assign adc_o = sd_signal;
localparam integer alpha_q15_int = alpha_q15_from_rc(R_OHM, C_PF, 15000000);
localparam signed [15:0] alpha_q15 = alpha_q15_int[15:0];
localparam signed [15:0] alpha_q15_top = alpha_q15 & 16'hff00;
sigmadelta_rcmodel_q15 #(
.alpha_q15(alpha_q15_top)
) rc_model (
.clk(clk_15), .resetn(resetn),
.sd_sample(sd_signal),
.sample_q15(raw_sample_q15)
);
lpf_iir_q15_k #(
.K(10)
) lpf (
.clk(clk_15), .rst_n(resetn),
.x_q15(raw_sample_q15),
.y_q15(lpf_sample_q15)
);
decimate_by_r_q15 #(
.R(375), // 15MHz/375 = 40KHz
.CNT_W(10)
) decimate (
.clk(clk_15), .rst_n(resetn),
.in_valid(1'b1), .in_q15(lpf_sample_q15),
.out_valid(signal_valid), .out_q15(signal_q15)
);
endmodule

5
rtl/util/conv.vh
View File

@@ -1,6 +1,3 @@
`ifndef CONV_VH
`define CONV_VH
// ============================================================================= // =============================================================================
// Convert Q1.15 to a biased UQ0.16 signal // Convert Q1.15 to a biased UQ0.16 signal
// ============================================================================= // =============================================================================
@@ -12,5 +9,3 @@ begin
q15_to_uq16 = biased[15:0]; q15_to_uq16 = biased[15:0];
end end
endfunction endfunction
`endif

95
rtl/util/rc_alpha_q15.vh
View File

@@ -7,82 +7,61 @@
`define RC_ALPHA_Q15_VH `define RC_ALPHA_Q15_VH
function integer alpha_q15_from_rc; function integer alpha_q15_from_rc;
input integer R_OHM; // ohms input integer R_OHM; // resistance in ohms
input integer C_PF; // picofarads input integer C_PF; // capacitance in picofarads
input integer FS_HZ; // Hz input integer FS_HZ; // sampling frequency in Hz
// Choose QN for x. N=24 is a good balance for accuracy/width. integer N; // fractional bits for x (QN)
integer N; reg [127:0] num_1e12_sllN;
reg [127:0] denom_u;
// We'll keep everything as unsigned vectors; inputs copied into vectors first. reg [127:0] x_qN; // x in QN
reg [63:0] R_u, C_u, FS_u; reg [255:0] x2; // x^2 in Q(2N)
reg [383:0] x3; // x^3 in Q(3N)
// x = 1 / (Fs * R * C) with C in pF -> x = 1e12 / (Fs*R*C_pf)
// x_qN = round( x * 2^N ) = round( (1e12 << N) / denom )
reg [127:0] NUM_1E12_SLLN; // big enough for 1e12 << N
reg [127:0] DENOM; // Fs*R*C
reg [127:0] X_qN; // x in QN
// Powers
reg [255:0] X2; // x^2 in Q(2N)
reg [383:0] X3; // x^3 in Q(3N)
integer term1_q15;
integer term2_q15;
integer term3_q15;
integer acc;
integer term1_q15; // x -> Q1.15
integer term2_q15; // x^2/2 -> Q1.15
integer term3_q15; // x^3/6 -> Q1.15
integer acc; // accumulator for result
begin begin
// Choose QN for x. N=24 is a good balance for accuracy/width.
N = 24; N = 24;
// Copy integer inputs into 64-bit vectors (no bit-slicing of integers) // x = 1 / (Fs * R * C) with C in pF ==> x = 1e12 / (Fs * R * C_PF)
R_u = R_OHM[31:0]; // x_qN = round( x * 2^N ) = round( (1e12 << N) / denom )
C_u = C_PF[31:0]; num_1e12_sllN = 128'd1000000000000 << N;
FS_u = FS_HZ[31:0];
// Denominator = Fs * R * C_pf (fits in < 2^64 for typical values) // denom = Fs * R * C_PF (fits in 64..96 bits for typical values)
DENOM = 128'd0; denom_u = 0;
DENOM = FS_u; denom_u = denom_u + FS_HZ[127:0];
DENOM = DENOM * R_u; denom_u = denom_u * R_OHM[127:0];
DENOM = DENOM * C_u; denom_u = denom_u * C_PF[127:0];
// // Guard: avoid divide by zero // rounded divide for x_qN
// if (DENOM == 0) begin x_qN = (num_1e12_sllN + (denom_u >> 1)) / denom_u;
// alpha_q15_from_rc = 0;
// disable alpha_q15_from_rc;
// end
// Numerator = (1e12 << N). 1e12 * 2^24 ≈ 1.6777e19 (fits in 2^64..2^65),
// so use 128 bits to be safe.
NUM_1E12_SLLN = 128'd1000000000000 << N;
// x_qN = rounded division
X_qN = (NUM_1E12_SLLN + (DENOM >> 1)) / DENOM;
// Powers // Powers
X2 = X_qN * X_qN; x2 = x_qN * x_qN; // 128x128 -> 256
X3 = X2 * X_qN; x3 = x2 * x_qN; // 256x128 -> 384
// Convert terms to Q1.15: // term1 = x -> shift from QN to Q15
// term1 = x -> shift from QN to Q15 term1_q15 = (x_qN >> (N - 15)) & 16'hFFFF;
term1_q15 = (X_qN >> (N - 15)) & 16'hFFFF;
// term2 = x^2 / 2 -> Q(2N) to Q15 and /2 // term2 = x^2 / 2 -> shift from Q(2N) to Q15 and divide by 2
term2_q15 = (X2 >> (2*N - 15 + 1)) & 16'hFFFF; term2_q15 = (x2 >> (2*N - 15 + 1)) & 16'hFFFF;
// term3 = x^3 / 6 -> Q(3N) to Q15, then /6 with rounding // term3 = x^3 / 6 -> shift from Q(3N) to Q15, then divide by 6 (rounded)
begin : gen_t3 begin : gen_term3
reg [383:0] tmp_q15_wide; reg [383:0] tmp_q15_wide;
reg [383:0] tmp_div6; reg [383:0] tmp_div6;
tmp_q15_wide = (X3 >> (3*N - 15)); tmp_q15_wide = (x3 >> (3*N - 15));
tmp_div6 = (tmp_q15_wide + 6'd3) / 6; tmp_div6 = (tmp_q15_wide + 6'd3) / 6; // +3 for rounding
term3_q15 = tmp_div6[15:0]; term3_q15 = tmp_div6[15:0];
end end
// Combine and clamp // Combine: alpha_q15 = x - x^2/2 + x^3/6 ; clamp to [0, 0x7FFF]
acc = term1_q15 - term2_q15 + term3_q15; acc = term1_q15 - term2_q15 + term3_q15;
if (acc < 0) acc = 0; if (acc < 0) acc = 0;
else if (acc > 16'h7FFF) acc = 16'h7FFF; else if (acc > 16'h7FFF) acc = 16'h7FFF;
alpha_q15_from_rc = acc; alpha_q15_from_rc = acc;
end end

37
sim/tb/tb_sigmadelta.v
View File

@@ -13,24 +13,39 @@ module tb_sigmadelta();
initial begin initial begin
$dumpfile("out.vcd"); $dumpfile("out.vcd");
$dumpvars; $dumpvars;
#2_000_000 #1_000_000
$finish; $finish;
end; end;
wire sd_a; wire sd_a;
wire sd_b; wire sd_b;
wire sd_o; wire sd_o;
wire signed [15:0] decimated_q15; // 3K3R 220PC 15MHZT
wire decimated_valid; sigmadelta_sampler sd_sampler(
.clk(clk),
.a(sd_a), .b(sd_b),
.o(sd_o)
);
sigmadelta_input #( wire signed [15:0] sample_q15;
.R_OHM(3300), sigmadelta_rcmodel_q15 rc_model(
.C_PF(220) .clk(clk), .resetn(resetn),
) dut( .sd_sample(sd_o),
.clk_15(clk), .resetn(resetn), .sample_q15(sample_q15)
.adc_a(sd_a), .adc_b(sd_b), .adc_o(sd_o), );
.signal_q15(decimated_q15),
.signal_valid(decimated_valid) wire signed [15:0] y_q15;
lpf_iir_q15_k #(9) lpf(
.clk(clk), .rst_n(resetn),
.x_q15(sample_q15),
.y_q15(y_q15)
);
wire signed [15:0] decimated_q15;
decimate_by_r_q15 #(400, 10) decimate(
.clk(clk), .rst_n(resetn),
.in_valid(1'b1), .in_q15(y_q15),
.out_valid(), .out_q15(decimated_q15)
); );
endmodule endmodule